Number of turns per game can be adjusted in the "Game Limits" in the "Choose-Your-Civ" screen. If you want a longer game than 540 turns, you can simply increase the total number of turns-in-game (up to a maximum of 1000, I think?), without modding anything else.
However, in order to preserve your accustomed tech-pace (i.e. relative to game-date), you would likely also need to go into the Editor and create a modified .biq file. There are at least 2 possible options that I can think of, which could probably also be combined to some extent.
The 'simpler' version would be to make some/ most/ all the techs untradeable, meaning that every player would have to spend longer to research everything themselves (or steal techs from rivals). This should substantially slow down the tech-pace, unless you also reduce some/all of the tech base-costs, making them cheaper/quicker to research (or steal? Not sure if that's related to tech-cost or not).
Another possibility would be to shorten the "years per turn" in the .biq's General Settings, but increase the total turns per duration proportionally to cover the same number of in-game years. If you want to have discoveries coming in at roughly the same tech-pace as in the base-game, you would then also need to increase all the base-costs for the techs (especially the Ancient–Medieval era techs), proportionally to the number of turns you're expecting to spend in those eras. This would likely take a lot more fine-tuning.
Bear in mind also that the "Wonder+Improvement-Culture-doubling" mechanic is hardcoded to trigger 1000 years after completion, according to the in-game date — so if you want to continue to have the 100K and 20K Culture victory conditions potentially happening at roughly the same end-dates, the Cultural values of buildings and Wonders may also need tweaking.